Vibrio cholerae is a human pathogen which colonizes small intestines of host, resulting in the onset of a severe diarrheal disease known as cholera. In order for V. cholerae to successfully colonize the host, it must express a series of virulence factors, which have been the main focus of the cholera research. However, bacterial pathogenicity is a multifactorial property in vivo that involves host response to infection, and gu microbiome interference of colonization. For example, although the pathology of cholera is not immune driven, it has been shown that minor, but significant inflammation responses in cholera patients and in experimental animal models are induced by V. cholerae infection and likely play a role in the resolution of disease. Little is known how inflammation is induced by V. cholerae and how V. cholerae copes with these signals and help its colonization. Here we performed an RNAseq analysis on mouse intestines free of V. cholerae and those that were infected to determine host responses to V. cholerae infection. One gene involved in reactive oxygen species (ROS) production, Duox2, encoding an NADPH oxidase and has been shown to be essential for controlling the growth of gut flora, was strongly upregulated. We show that both Duox2 expression and ROS production are induced by V. cholerae in a tissue culture model and in mice. Interestingly, this induction is dependent on V. cholerae virulence gene expression. Moreover, our preliminary studies indicate that V. cholerae cells in cholera patients' stool samples are highly resistant to ROS, suggesting that V. cholerae undergoes induction of ROS resistance during infection. To elucidate how V. cholerae overcome ROS produced by the host, we performed a Tn-seq experiment and found a set of V. cholerae genes that are required for ROS resistance in vivo. Together with a proteomics approach, we reveal novel transcriptional and posttranslational regulation mechanisms that are involved in regulating ROS resistance. Therefore we hypothesize that during infection, V. cholerae induces host Duox2 expression, thus ROS production, which facilitate V. cholerae colonization by modulating gut flora composition, whereas transcriptional and posttranslational regulatory pathways lead to V. cholerae inherently resistant to ROS in vivo. We will investigate the mechanism of V. cholerae-induced host ROS production and its effects on gut microbiota composition and V. cholerae colonization. We will investigate V. cholerae ROS resistance during infection of an adult mouse model. We will focus on transcriptional regulation and posttranslational modification of cellular functions of ROS resistance. Finally, we will investigate V. cholerae ROS resistance mechanisms in cholera patients by performing RNAseq and proteomic analysis of V. cholerae cells directly from cholera patient vomituses and stools.